Biofouling has always been problematic in industrial water systems such as cooling towers, heat exchangers and air washers, because it can adversely affect heat transfer efficiency and fluid frictional resistance, thereby subsequently reducing production rates. In addition, biofouling also plays an important role in microbiologically influenced corrosion.
The presence of microorganisms in industrial waters cannot be totally eliminated, even with the excessive use of chemical biocides. The most common way to control biofouling is through the application of toxic chemical biocides such as chlorine, bromine, isothiazolones, glutaraldehyde or other antimicrobials. These biocides arc added in an attempt to kill both planktonic and attached microorganisms.
Some microorganisms attach to inert surfaces forming aggregates with a complex matrix consisting of extracellular polymeric substances (EPS). This consortium of attached microorganisms and the associated EPS is commonly referred to as a biofilm. Biocides have difficulty penetrating biofilms and removing them from surfaces. Although excessive biocide dosages may be able to control biofouling, the presence of biocides in effluent waters is usually environmentally unacceptable.
Mechanical treatments including scrapers, sponge balls, or "pigs" are also commonly used to remove biofilms. Acids, chelants and dispersants are likewise considered to be effective in causing the detachment of deposited materials. In addition, sidestream filtration devices, which continuously process 1-5% of the system water, have drawn increased interest lately. Nevertheless, these approaches are either too labor intensive and/or expensive.
Dispersants are sometimes applied along with biocides to enhance antimicrobial efficacy in industrial waters. The dispersants used in these applications will hereinafter be referred to as "biodispersants." Most biodispersants currently available on the market, such as block copolymer or terpolymer, have high molecular weights ranging from 1,000 to 15,000,000. These biodispersants attract fine foulant particles onto polymeric chains and form fluffy particles that are more readily detached from the fouled surfaces. It is also believed that these surface active compounds can increase the diffusion of biocide into the biofilm, and subsequently cause biofilm detachment.
To date, biodispersants have not been used effectively without supplementation with biocides. As the United States Environmental Protection Agency (EPA) regulations and global concerns of biocide usage become more prevalent, high performance biodispersants having low toxicity are needed to control biofouling either with or without the addition of chemical biocides.
Accordingly, it would be desirable to provide a method of removing biofilms from surfaces submerged in water using a biodispersant which is effective both alone and with the use of a biocide. It would also be desirable to utilize a biodispersant which is biodegradable and has a low toxicity. It would furthermore be desirable to employ a biodispersant which does not affect corrosion and scale inhibition programs used in industrial water treatment.